Composite structure for the fluorimetric monitoring of functional coatings

ABSTRACT

A method for monitoring the coating weight, uniformity, defects or markings present in a coating of a composition applied to a substrate comprises the steps: 
     a) providing a substrate with a functional coating of a composition comprising an effective amount of uvescer that absorbs radiant energy, i.e., has an excitation energy, of wavelength λ 1  and emits radiant energy of wavelength λ 2  ; 
     b) scanning the coating with radiant energy having a wavelength within wavelength λ 1  ; 
     c) detecting the radiant energy of wavelength λ 2  emitted by the coating; and 
     d) optionally, correlating the emitted radiant energy to independently measured standard coating weights or thicknesses, of the coating so as to measure coating weight, thickness, uniformity, defects, or markings.

This is a division of application Ser. No. 07/711,366 filed Jun. 5,1991, now U.S. Pat. No. 5,270,116, which is a continuation of Ser. No.07/220,991, filed Jul. 13, 1988, now abandoned, which is a continuationin part of Ser. No. 06/883,926, filed Jul. 10, 1986, now abandoned.

FIELD OF THE INVENTION

The present invention relates to a method of detecting thickness,uniformity, and defects in coatings and detecting marking in coatingsthat have been applied to substrates, utilizing uvescence, i.e.,fluorescence in the ultraviolet region of the electromagnetic spectrum.In another aspect it relates to uvescing compounds suitable for such useand compositions containing them.

BACKGROUND ART

Very few articles of commerce and general use do not have a coating ofsome kind for the enhancement of appearance, scratch and abrasionresistance, moisture proofing, adhesion or release of other materials,or alteration of some other characteristics of the surface of thearticle. Since the quality and cost of the coating is dependent on thecoating weight and uniformity it is desirable that a means formonitoring these characteristics be employed.

The use of radiation to measure thickness of coatings has been taught.U.S. Pat. Nos. 3,019,336 and 3,130,303 disclose that beta rays emanatingfrom a radioactive source such as strontium-90 and directed toward acoating are backscattered in an amount related to the thickness of thecoating. Such a technique cannot be used to monitor coating uniformityand coating defects during manufacture of web materials bearing thincoatings. In this technique only the average coating weight can bedetermined, not the weight at any specific point.

U.S. Pat. Nos. 3,675,015, 3,118,060, 3,930,063, 3,956,630 and 4,250,382disclose methods and apparatus for continuously monitoring coatingweight of a coating on a web or fiber. For these methods, a fluorescingcompound, dye or pigment, is added to the coating formulation and thefluorescence of the coating in the visible range of the electromagneticspectrum is continuously and quantitatively measured while the coatingis exposed to ultraviolet radiation. Fluorescence readings taken in thecross direction and machine direction of the web give an indication ofthe lay of the coating on the web. These techniques, although useful formonitoring coatings on some webs, e.g. paper or fiber, are notsatisfactory for monitoring coatings on webs which also fluoresce, suchas paper treated with an optical brightener to enhance whiteness.Further, it isostated in U.S. Pat. No. 4,250,382 (col. 2, lines 10-12)that fluorescent dyes have not been found satisfactory for detectingcoatings of cured polysiloxane resins.

SUMMARY OF THE INVENTION

The present invention, which provides a method for monitoring afunctional coating composition applied to a substrate, comprises thesteps:

a) providing a substrate with a functional coating of a compositioncomprising an effective amount of a uvescer that is an organic orinorganic compound that absorbs radiant energy, i.e., has an excitationenergy, of wavelength λ₁ and emits radiant energy of wavelength λ₂ ; λ₁and λ₂ each being wavelengths within the ultraviolet portion of theelectromagnetic spectrum;

b) scanning the coating with radiant energy having a wavelength withinthe range of wavelength λ₁ ; and

c) detecting the radiant energy of wavelength λ₂ emitted by the coating;and

d) optionally, correlating the emitted radiant energy to independentlymeasured weights or thicknesses of the coating.

The functional coating composition of the invention can be monitored fordefects, average weight, uniformity, markings as for registry,alignment, images, or coded information by the method of the invention.

Prior art coatings which depend on luminescent components for monitoringprovide extraneous light when the article is viewed. This light willchange appearances and color fidelity in an article. In contrast,coatings of the present invention which utilize uvescers (which do notemit visible light) cannot change the appearance or color fidelity of anarticle.

The instant invention is particularly useful when the substrate to whicha coating is being applied is one that fluoresces (contains aluminescer), i.e., absorbs radiant energy of a wavelength in theultraviolet and emits most or all of its radiation in the visible and/ornear ultraviolet portion of the electromagnetic spectrum. The substratefluorescence in the instant invention does not mask the ultravioletemission of the coating.

Prior art coatings applied to substrates that fluoresce cannot beaccurately monitored in the visible range because of interference by thesubstrate fluorescence which masks the visible emission of the coating.In contrast, coatings of the present invention function satisfactorilyon substrates that fluoresce in the visible range because emission ismonitored in the ultraviolet range.

In another aspect of the invention, there are provided functionalcoating compositions that can be monitored for thickness, uniformity,and defects. The invention also provides substrates bearing a layer ofsuch compositions including discontinuous coatings such as marks,images, or coded information.

Uvescers useful in the invention generally absorb radiant energy ofwavelength λ₁, which is in the ultraviolet range. The wavelength shouldgenerally be below 400 nm and should generally be above 240 nm becausethis minimizes interference from any visible radiation emitted by thesubstrate; the uvescer emits in a wavelength λ₂, which generally is lessthan 430 nm with no more than 30 percent of the emitted light having awavelength greater than 400 nm and preferably is less than 350 nm. Thisallows for minimization of interference from any visible radiation thatmay be emitted by the substrate.

The process of the invention is particularly desirable for thosecoatings having a utility that requires expensive components and/or forwhich coating thickness and uniformity are critical, especially whereloss as a result of flaws and of non-optimal coating weight cannot betolerated. Generally, such coatings can be from about 0.01 to about 200or more micrometers in thickness, and for release coatings 0.01 to 10micrometers may be preferred. Examples of such functional coatingcompositions include primer coatings for enhancing the adhesion ofsubsequently applied top coatings; protective coatings such as moistureresistant and abrasion-resistant coatings; radiation-sensitive imageablelayers; adhesive coatings such as those based on synthetic and naturalrubber, acrylic, epoxy, and silicone compounds; and release or abherentcoatings such as those based on polymers of long chain aliphaticcompounds, silicone resins and fluorochemicals.

Prior art coatings which depend on luminescent components for monitoringemit visible light when the article is viewed. As noted above, thislight will change color fidelity of the article.

In contrast, the present invention provides for monitoring by means ofuvescers which emit most of their energy in the ultraviolet range. Theamount of visible light emitted is small and hence cannot modify oralter the color of the article.

In this application:

"fluorescence" means emission of a photon from a substance, occurring asa result of a spin conserving transition from an excited electronicstate to a lower energy electronic state;

"phosphorescence" means the emission of a photon from a molecule,occurring as a result of a non-spin conserving transition from anexcited electronic state to a lower energy electronic state;

"uvescence" means fluorescent or phosphorescent emission in theultraviolet portion of the spectrum;

"luminescence" means fluorescent or phosphorescent emission in thevisible portion of the spectrum;

"uvescer" means a uvescent compound or substance which bears a uvaphoregroup or radical which on illumination by radiation in the ultravioletportion of the spectrum emits ultraviolet radiation and differs fromluminescent compounds of the prior art which emit light in the visibleportion of the spectrum above about 400 nm;

"functional coating composition" is a term applied to any coatingcomposition having utility;

"organic" means any compound including an organic group, e.g., anorganometallic compound; and

"uvaphore" means a group or radical which may be mono- or polyvalent,which confers uvescence upon a monomeric compound or polymer comprisingit.

DETAILED DESCRIPTION OF THE INVENTION

The functional coating composition comprises (1) a monomeric orpolymeric composition that can be thermoplastic and/or curable thatprovides the characteristics necessary to produce the function of thecoating and adjuvants for modifying these characteristics, (2) aneffective amount of a uvescer that (a) absorbs radiant energy ofwavelength λ₁, (b) emits radiant energy of wavelength λ₂, λ₁ and λ₂ eachbeing wavelengths or ranges of wavelengths within the ultravioletportion of the electromagnetic spectrum, and the mean of the range of λ₂is above the mean of the range of λ₁ in the electromagnetic spectrum.

In one embodiment, λ₁ represents one or more wavelengths in the range of240 to 400 nm, and λ₂ represents a range of wavelengths of the emittedradiant energy below about 430 nm, not more than 30% of which has awavelength above 400 nm, and preferably is in the range of 280 to 400nm, and most preferably 290 to 350 nm. In the case of a uvescer, thecoating composition has a product (εφ) of molar extinction (molarabsorptivity) coefficient (ε) and quantum yield (φ) of at least 1000.Preferably, the product (εφ) is 10,000 or more. (ε) and (φ) are definedin A. J. Gordon et al. "The Chemist's Companion", Wiley-IntersciencePublication, John Wiley & Sons, New York (1972), particularly pages 211and 362.

The product of the molar extinction coefficient and the quantum yield isa measure of the efficiency of a uvaphore, the greater the product thehigher the efficiency of the uvaphore. The preferred ranges allow forminimal interference from any visible radiation emitted by thesubstrate.

Uvescers which absorb radiation in the range of 240 to 290 nm and emitradiation in the range of 290 to 350 nm do not absorb solar ultravioletradiation which is in the range of 295 to 400 nm. These uvescers thushave the advantage in contrast to prior art luminescers, that theycannot act as sensitizers for the solar photodegradation of a coating orsubstrate.

Substrates to which the coating composition of the invention can beapplied include any solid surface, for example, those of paper,cardboard, wood, cork, plastic such as polyester, polyurethane,polyamide, polycarbonate, polyolefin, etc., woven and nonwoven fabricsuch as cotton, polyester, polyolefin, nylon, etc., metals such asaluminum, iron, etc. glass, fused silica, ceramic, etc., includingfabrics made therefrom. Substrates which are continuous webs or fibersare particularly applicable to the process of the invention and may beinspected "on-line" to permit continuous control of the processvariables.

Substrates that fluoresce or phosphoresce above about 350 nm,particularly those that fluoresce or phosphoresce in the visible range(about 400 to 700 nm), contain in their structure components thatluminesce. These components are commonly aromatic in character, i.e.,the component is a group that is more or less similar in character tobenzene and can be hydrocarbyl or heterocyclic. Examples of aromaticgroups that, when properly substituted, may be luminescent are phenyl,naphthyl, quinolyl, pyridyl, furyl, etc., and their correspondingpolyvalent groups. other components of substrates that can fluoresce orphosphoresce in the visible portion of the optical spectrum areluminescent inorganic pigments such as Y₂ O₃ : Eu, YVO₄ :Eu, La₂ O₂ S:Eu, and Zn₃ Cd₂ S:Ag, and powders of minerals such as willemite, amongmany others.

Uvescers used in the coating composition and process of the inventionshould be capable of being stably dispersed (i.e., dissolved or finelydivided such that on dispersing in a functional composition a suspensionis formed from which less than ten percent by weight of the particlessettle out in 24 hours) into a functional composition; preferably, theuvescers are soluble in the coating; and most preferably, the uvescersare reacted into the coating and become chemically bound as uvaphorestherein. The material preferably is organic, i.e., it can be aromatic,aliphatic, heterocyclic, cycloaliphatic, or inorganic. As used herein,organic includes organometallic. In addition to carbon and hydrogen, theuvescer can contain one or more elements of groups 2-17 (formerly oftencalled IIA-VIIB) of the Periodic Table of Elements as described in Chem.and Eng. News 63 (No. 5) Feb. 4, 1985 as for example oxygen, nitrogen,sulfur, chlorine, titanium, boron, vanadium, chromium, manganese,cobalt, copper, zinc, and silicon. The uvescer can be monomeric or apolymeric compound having a molecular weight of up to 500,000 or more,including crosslinked polymers.

    ______________________________________                                        Examples of Monomeric Uvescers include:                                                                εφ                                       ______________________________________                                        biphenyl                 2,900                                                4-methylbiphenyl         8,000                                                4-benzylbiphenyl         4,800                                                4-vinylbiphenyl          18,300                                               4-phenoxybiphenyl        2,200                                                1,3,5-triphenylbenzene   16,200                                               indole                   2,200                                                azulene                  1,150                                                naphthalene              1,400                                                2-chloronaphthalene      2,500                                                2-naphthol               1,100                                                acenaphthene             4,400                                                fluorene                 19,200                                               dibenzofuran             8,500                                                carbazole                1,700                                                N-butylcarbazole                                                              N-ethylcarbazole                                                              m-terphenyl              13,100                                               p-terphenyl              31,600                                               4-methyl-p-terphenyl     32,000                                               p-quaterphenyl           35,600                                               2,5-diphenylfuran        38,000                                               2,5-diphenyl-1,3,4-oxadiazole                                                                          24,900                                               2-phenyl-5-diphenyl-1,3,4-oxadiazole                                                                   39,800                                               2-phenyl-5-(2-naphthyl)-1,2,3-oxadiazole                                                               9,700                                                triphenylene             1,700                                                dibenzothiophene         300                                                  dibenzothiophene-9,9-dioxide                                                  9,10-dihydrophenanthrene                                                      ______________________________________                                    

Also intended are derivatives of these uvescers which bear functionalgroups such as vinyl, vinyloxy, allyl, hydroxy, amino, carboxy, epoxy,isocyanato, acryloxy, methacryloxy, acrylamido, and hydrosilyl groups.

Compositions of the invention that are preferred comprise (1) afunctional coating composition comprising a polymeric compound orpolymer precursor and (2) an effective amount of a uvescent substance ormore preferably of a uvaphore having attached to it one or more groupsthat increase the dispersibility of the uvescer in the functionalcoating composition, the substituted uvescer having the general formula##STR1## wherein R is a group comprising at least one uvaphore andhaving a valence "a", the uvaphore being a polycyclic aromatic group andhaving two to four aromatic rings of which at least two are joined by asingle bond (e.g., as are present in biphenyl, bipyridyl,2,5-diphenylfuran, etc.) or by fusion (e.g., naphthalene, fluorene,carbazole, dibenzofuran, etc.), the polycyclic aromatic compoundabsorbing radiant energy of wavelengths between 240 and 400 nm, emittingradiant energy below about 430 nm, no more than 30% of the emittedenergy being above 400 nm, and having an εφ product of at least 1000,preferably in excess of 10,000; R can comprise 1 to 5 uvaphores,preferably no more than 2;

each X is independently hydrogen or B, and preferably one B group ispresent, in which B is a reactive group that can react to form acovalent bond with a complementary reactive group present in the polymeror polymer precursors; examples of B include a vinyl group --CH═CH avinyloxy group --OCH═CH₂, a carboxyvinyl group ##STR2## an allyl group--CH₂ CH═CH₂, a hydroxy group --OH, an amino group --NH₂, a carboxygroup --COOH, an epoxy group ##STR3## a glycidyloxy group ##STR4## anisocyanato group --NCO, an acryloxy group ##STR5## a methacryloxy group##STR6## an acrylamido group ##STR7## or a hydrosilyl group --Si(R³)₂ Hin which R³ is independently a methyl, ethyl, or phenyl group,

R¹ is an alkylene or alkenylene group, preferably being omegaunsaturated, the group having 1 to 18 carbon atoms;

a is an integer having a value from one to three, inclusively; and

b is zero or one, b being one when X is hydrogen.

Examples of preferred uvescers for functional coating compositionsinclude the following compounds and their derivatives:

4-butylbiphenyl

N-pentylindole

1-heptylnaphthalene

1-vinylnaphthalene

2-(5-hexenyl)naphthalene

1-naphthalenecarboxylic acid

1-naphthaleneneisocyanate

2-(5-isocyanatopentyl)naphthalene

1-(7-octenyl)naphthalene

1-trimethylsilylacenaphthylene

1-aminonaphthalene

1-acrylamidonaphthalene

2-acryloyloxynaphthalene

2-methacryloyloxynaphthalene

9-[(2-acryloyloxy)ethylcarbamoyl]-9H-fluorene

biphenyl

triphenylbenzene

fluorene

carbazole

terphenyl

quaterphenyl

triphenylene

naphthalene

2,5-diphenylfuran

dibenzofuran

2,5-diphenyl-1,2,4-oxadiazole

2,3-epoxypropoxynaphthalene

4-heptyl-p-terphenyl

4-(undec-10-enoyl)-p-terphenyl

9-butylcarbazole

9-heptylcarbazole

9-allylcarbazole

9-(7-octenyl)carbazole

3-decylcarbazole

4-butyl-p-quaterphenyl

2-phenyl-5-(4-butylphenyl)furan

2,5-bis(4-butylphenyl)oxadiazole

2-hexyltriphenylene

9-isocyanatofluorene

dimethyl-1-naphthylsilane

9-allyfluorene

9-butylfluorene

4-butylfluorene

9-(7-octenyl)fluorene

Uvescers that are particularly preferred for use in the compositions ofthe invention are polymeric uvescers that are organic condensation oraddition polymers having one or more terminal or pendent uvaphore groupsattached to a polymeric backbone, the pendent uvaphore group having theformula ##STR8## wherein R is the same as defined above in Formula I,

R² is an alkylene or alkenylene group having 1 to 18 carbon atoms,

Y is a carbon-to-carbon single bond or a divalent connecting groupresulting from the reaction of a reactive group attached to the uvaphorewith a complementary reactive group present in the condensation oraddition polymer; representative Y groups include an oxycarbonyl group,##STR9## as is formed by reaction of a hydroxy group-containing polymerand a carboxy group attached to the uvaphore; a carbonyloxy group##STR10## that is formed by the reaction of a carboxy group-containingpolymer and a hydroxy group attached to the uvaphore; a urethane group,##STR11## that is formed by the reaction of a hydroxy group-bearingpolymer and an isocyanato group-bearing uvaphore; a3-oxy-2-hydroxypropoxy group, --OCH₂ CH(OH)CH₂ O--, that is formed bythe reaction of a hydroxy group-bearing polymer and a 2,3-epoxypropoxygroup-bearing uvaphore, a silylethyl group such as --CH₂ CH₂ --Si(CH₃)₂-- that is formed by the reaction of a vinyl substituted polymer and adimethyl-hydrosilyl group-bearing uvaphor, and

a is an interger of 1 to 3 inclusively, and

b is zero or one.

Polymeric uvescers can be prepared by the reaction of a condensation oraddition polymer that is to be used as the polymer or polymer precursorfor a functional coating with a uvescer bearing a reactive groupcomplementary to the reactive group of the polymer or precursor.Examples of such polymeric uvescers include polyvinylcarbamates,polyacrylates, polysiloxanes, polyethers, perfluoropolyethers, andpolyesters. Specific examples of such polymeric uvescers include:

1. Polyvinylcarbamates.

The reaction product of a partially hydrolyzed polyvinylacylate,9-isocyanatofluorene and octadecylisocyanate, the average polymer havingthe formula, wherein the units can be randomly arranged, ##STR12## inwhich R⁶ is one or more of lower alkyl groups (C₁ to C₄) or a phenylgroup, and c, d, and e are integers the sum of which is about 10 to20,000, d is 0.01% to 10% of the sum and e is 5% to 95% of the sum.Coatings of such polymers on substrates, e.g., kraft paper, polyester,polyolefin, cellulose acetate, polyolefin coated papers, and the likecan function as a low adhesion backsize that can be monitored forthickness and coating defects by the process of the invention.

2. Polyacrylates.

The reaction product of a polymer of one or more acrylic esters ofnon-tertiary alkanols having 4 to 12 carbon atoms and one or more ofacrylic acid, methacrylic acid, or itaconic acid with2-(5-isocyanatopentyl)-naphthalene, the polymer having randomly arrangedunits in an average formula of the structure: ##STR13## in which R⁴ is aprimary or secondary alkyl group having 4 to 12 carbon atoms and R⁵ ishydrogen, methyl, or carboxymethyl and f, g, and h are numbers the sumof which is about 10 to 20,000, g is 0.01 to 10% of the sum and h is 0to 75% of the sum. Coatings of such polymers are functional aspressure-sensitive adhesives that can be monitored for thickness andcoating defects by the process of the invention.

3. Polysiloxanes.

The hydrosilation reaction product of hydride-functionalpolydimethylsiloxane fluids with 9-allyl fluorene having the averageformula, wherein the units can be randomly arranged. ##STR14## in whichj, k, and m are numbers the sum of which is about 10 to 10,900, k beingfrom about 0.01 to 10% of the sum of j, k and m, m being from zero toabout 99.5% of the sum of j, k and m, and n being a number from about 5to 10,000. Such polymers, if contained in coatings on a substrate, arefunctional as release surfaces, or they can be dispersed inpolysiloxanes to form compositions that can be coated and monitored forthickness, uniformity, and defects by the process of the invention.

4. Perfluoropolyethers.

The reaction product of 9-aminofluorene with a dimethylester terminatedperfluoropolyether, the average polymer having the formula: ##STR15## inwhich integers p and q designate the number of randomly distributedperfluoroethyleneoxy and perfluoromethyleneoxy backbone repeatingsubunits respectively, the ratio p/q being 0.2/1 to 5/1, said compoundshaving a number average molecular weight in the range of 500 to 20,000or higher, preferably 800 to 15,000.

5. Polyethers.

The reaction product of a functional group substituted uvescer such as,for example, 9-isocyanatofluorene and polyoxyalkylenepolyols, such asthe reaction product of 9-isocyanatofluorene with the ethyleneoxideadduct of a polyol having an average formula of the structure ##STR16##in which p designates the number of ethyleneoxy units and is a numberfrom 1 to 30 or more, R is hydrogen or an alkyl, cycloalkyl,heterocyclic, or aryl group having a valence of s and s is an integer of1 to 6 and, preferably, the reaction product has a molecular weight of15 to 1000.

6. Polyesters.

The reaction product of one or more dicarboxylic acids and one or morepolyols having from 2 to 6 hydroxyl groups in which at least one of thedicarboxylic acids and/or polyols is substituted by a uvaphore group toprovide in the polyester uvescer a concentration of about 1 to 50% byweight uvaphore. An example of such a polyester uvescer is the reactionproduct of diethyleneglycol and 2,5-bis(4-carboxyphenyl)furan and adipicacid. The reaction product has the average formula of the structure:##STR17## in which v designates the number of uvaphore ester units inthe reaction product and is a number from 1 to about 20 and w designatesthe number of ethyleneoxyethylene adipate units in the reaction productand is zero or a number up to about 30 and the molecular weight of thereaction product is from about 300 to 10,000.

Monomeric uvescers can be present in an amount in the range of 0.001 to10 weight percent, preferably 0.01 to 5 weight percent of the coatingcomposition. Polymeric uvescers can be present in amounts up to 100% ofthe coating composition. Generally, the amount of polymeric uvescersused is such that the uvaphore component of the polymeric uvescers ispresent at a concentration of 0.001 to 10 weight percent of the totalcoating composition.

A maximum effective amount of a uvescer for measuring thickness is anamount sufficient to allow ultraviolet radiation to penetrate thecoating to its full depth and provide a maximal emitted signalconsistent with there being a measurable signal from the entire depth ofthe coating. Amounts in excess of an effective amount will tend toabsorb all of the ultraviolet radiation in the upper portion of thecoating and will provide no useful signal from the lower portion toindicate its thickness. Amounts less than the maximum effective amountmay be highly satisfactory or even preferred if it is desired that thecoating weight be directly proportional to the measured signal. Themaximum effective amount allows for measuring coating thickness as wellas for detecting coating voids. For detecting coating voids amounts ofuvescer may be substantially greater than the maximum effective amountuseful for measuring thickness.

To determine the maximum effective amount of uvescer for a particularapplication it is necessary to establish the range of coating thicknessfor which a measurement is desired. At the maximal thickness,ultraviolet radiation must penetrate to the base of the coating to asufficient degree to provide a useful signal. This can be established bycoating the uvescer-containing composition on a substrate transparent toultraviolet radiation and measuring the ultraviolet radiationtransmission of λ₁. The coating should have an absorbance no greaterthan 1.0 (the absorbance varies with thickness and amount of uvescer).For each application the maximum effective amount of uvescer should beindividually determined.

The compositions of the invention that can be monitored for thickness,uniformity, and defects and inspected for markings by the process of theinvention are prepared from any of the coating compositions known in thecoating art that are not opaque to radiant energy of λ₁ or λ₂ (e.g.,paints containing pigments such as titanium oxide and adhesivecompositions containing phenolic resins which would absorb more thanabout 90% of the radiant energy of λ₁ could not be monitored but anycoating transparent to more than about 10% of the radiant energy of λ₁could be monitored; these limits do not apply if only voids are to bedetected). There is added to the coating composition 0.001 to 10 weightpercent of the uvescer and the mixture is stirred or homogenized untilthe uvescer is uniformly dispersed or preferably is dissolved. In somecases, the uvescer reacts with the coating and becomes incorporatedtherein as a uvaphore. These are preferred embodiments of the presentinvention. The composition is then coated onto a substrate by anytechnique known in the art including spraying, curtain coating, director reverse roll coating, dipping, brushing, extruding, and printing. Thecoating may be continuous or discontinuous and can include images ormarkings intended as process signals or as coded product information.Solvent, when used, is then removed from the coating by air drying,heating, vacuum drying, etc. as is known in the art. Then, after orpreferably before curing by heat or exposure to actinic radiation (e.g.,ultraviolet, infrared, x-ray, etc.) or electron-beam, when desired, thecoated substrate is illuminated with radiant energy of a wavelength thatcan excite the uvescer into uvescence (energy in the ultraviolet withinthe range of λ₁) and the emitted energy of uvescence in the ultravioletportion of the spectrum, λ₂, measured. An instrument suitable for use inilluminating the coated substrate with excitation energy and measuringthe energy of uvescence is a fluorescence spectrophotometer such as themodel No. MPF-44B Fluorescence Spectrophotometer supplied byPerkin-Elmer, Norwalk, Conn. Illumination of the coated substrate canalso be provided by other sources of illumination known in the art suchas by use of xenon arcs, mercury arcs, ultraviolet lasers, and "blacklamps". The use of filters to isolate a particular wavelength is oftendesirable. The uvescent emission from the coatings can be measured bymeans of photodiodes or phototubes.

The emitted energy of uvescence is then correlated to coating weight orthickness of the coating as determined by an independent method such asgravimetric analysis, ash determination, ellipsometry, chemical, orradiochemical analysis, etc. A plot of emission energy versus coatingweight is then made. Readings on the graph provide a standard whichrepresents a correlation between uvescent emission and coating weightfor a particular coating. When the emission energy of the coatingdeviates from that for the desired coating thickness, the coatingprocess is adjusted to obtain the uvescent energy indicative of thedesired coating thickness.

Voids, variations in coating uniformity, and other defects occurring inthe coating are also made apparent by changes in the emission energy ofthe coating. Steps can then be taken to correct such undesirableoccurrences.

Substrates bearing functional layers or articles comprising functionallayers such as primer compositions, protective coatings such as moistureresistant or abrasion resistant coatings, adhesive coatings, lubricatingcoatings, radiation-sensitive imageable coatings, and release orabherent coatings can advantageously be coated with compositions of theinvention. Such uvescer-containing layers can be monitored, using themethod of the present invention, for coating thickness, uniformity, anddefects. Furthermore, any subsequent overcoatings may be monitored ifthey absorb some or all of either λ₁ or λ₂, since the presence of voidswill be readily detected, while thickness may be adjudged by the degreeof attenuation of the signal. This same principle can be used to providemarkings or images for the aforementioned purposes.

In addition, the presence of a first article which is to be adhered to asecond article can be ascertained if the first article comprises afunctional coating of the instant invention. For example, the presenceof a release liner on an article can be detected if the release linercomprises a uvescer as taught in the present invention.

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit the invention.

EXAMPLE 1

This example describes a solventless silicone release coatingcomposition containing a soluble, essentially non-volatile, reactiveuvescer; coating and curing the release composition on a substrate toyield release liners of varied coating weight; and analyzing the releaseliners on a fluorescence spectrophotometer to show the correlationbetween coating weight and uvescent emission level.

To a solution consisting of 99 g of a dimethylvinyl-chainstoppedpolydimethylsiloxane fluid with a viscosity of 350 cps and 1.0 g9-allylfluorene was added a platinum/vinyl siloxane catalyst (see U.S.Pat. No. 3,715,334, EXAMPLE 5) to provide 100 parts of platinum metalper 1,000,000 parts of silicone composition. After mixing for 10 min.,0.25 g 2-ethylhexylhydrogen maleate hydrosilation inhibitor was addedand the catalyzed inhibited silicone solution was mixed for anadditional 10 min. Next, there was added 2.5 g of atrimethylchainstopped polymethylhydrogen siloxane fluid having aviscosity of 70 cps. The resultant mixture was stirred for 15 min. moreto yield a solventless, thermally curable silicone release coatingcomposition containing a soluble, virtually non-volatile, reactiveuvescer.

The silicone coating composition was then applied to 60 lb. brownsuper-calendered kraft paper (weighing about 105 g/m²) at 4 coatingweights with a 3-roll differential speed offset gravure coater, equippedwith a 79 line/cm (200 line/inch) gravure cylinder, a rubber transferroll, and a steel back-up roll; the transfer and back-up rolls turned ata surface speed of 13.7 re/min (45 ft/min.), and the gravure roll turnedfirst at 4.1 re/min (13.5 ft/min.), then at 3.03 m/min (10.0 ft/min.),then at 2.69 m/min. (9.0 ft/min.), and finally at 2.02 m/min (6.75ft/min.) to provide 4 samples of different coating weights. These coatedsamples were cured in a forced air oven at 300° C. for 60 sec. toprovide 4 samples of release liners containing a chemically bounduvaphor. The resultant coating weights were determined by analysis on aPrinceton Gamma-Tech™ model No. 100 Fluorescent Chemical Analyzer,Princeton Gamma-Tech, Inc., Princeton, N.J. and the average of 5 valuesshowed the coating weights to be 1.22 g/m², 1.03 g/m², 0.96 g/m², and0.77 g/m² , respectively, as standard for correlation to uvescent dataof the invention. (Differential-speed coating of silicones is describedin U.S. Pat. No. 4,216,252).

The 4 samples of release liner thus prepared were analyzed on aPerkin-Elmer MPF-44B Fluorescence Spectrophotometer, Perkin-Elmer,Norwalk, Conn. utilizing an excitation wavelength of 260 nm whilemeasuring the uvescent emission level at a wavelength of 315 nm. Theuvescent emission level was measured 5 times for each sample and theaverage emission level for each coating weight is reported in Table I.

                  TABLE I                                                         ______________________________________                                                    Coating     Uvescent                                              Sample      weight (g/m.sup.2)                                                                        emission level                                        ______________________________________                                        1           1.22        85                                                    2           1.03        63                                                    3           0.96        46                                                    4           0.77        40                                                    ______________________________________                                    

The data of Table I show the strong correlation between coating weightand uvescent emission level: i.e., as coating weight decreases theuvescent emission level also decreases.

EXAMPLE 2

This example describes the preparation of an organic based thermoplasticrelease composition that contains a chemically bound uvaphore; coatingthe release composition on a substrate to yield release liners of variedcoating weight; and analyzing the release liners on a fluorescencespectrophotometer to show the correlation between coating deposition anduvescent emission level.

To a 1-liter 3-necked round-bottom flask equipped with a Dean-Starkwater trap, reflux condenser, static nitrogen atmosphere, and mechanicalstirrer was added 218 g xylene and 30 g of partially hydrolyzedpolyvinyl acetate with a degree of hydrolysis of about 50%. Thepolyvinyl acetate dispersion was azeotroped to dryness at atmosphericpressure before a solution containing 62.2 g octadecylisocyanate,(Mondur O™, Mobay Chem. Co., Pittsburgh, Pa.) and 0.94 g9-isocyanatofluorene was added to the flask and the reaction maintainedat reflux for 20 h. An aliquot removed from the flask and analyzed byinfrared spectroscopy showed only a trace of isocyanate remaining afterrefluxing 20 h. To the completed reaction solution was added 1551 gtoluene to yield a 5 wt percent solids solution of an organic-basedthermoplastic release composition containing a chemically bound uvaphor(see col. 9 of U.S. Pat. No. 2,532,011 for preparation ofpolyvinylcarbamates).

This solution was applied at a variety of coating weights to 50micrometers (2 mil) polypropylene film using wire wound stainless steelcoating rods (RDS coating rods, R.D. Specialties, Inc., Webster, N.Y.).RDS rod numbers 3, 4, 5, and 6, utilized for these coatings deposit wetfilm thicknesses of 6.9, 9.1, 11.4 and 13.7 micrometers (0.27, 0.36,0.45, and 0.54 mils) respectively. The coated samples were dried in aforced air oven at 700° C. for 5 min and were then analyzed as inEXAMPLE 1 on a fluorescence spectrophotometer using a λ₁ of 260 nm and aλ₂ of 315 nm. Two measurements were taken for each sample and theaverage uvescent emission level obtained for each coating weight isreported in Table II below.

                  TABLE II                                                        ______________________________________                                                     Coated with                                                                              Uvescent                                              Sample       RDS rod No.                                                                              emission level                                        ______________________________________                                        5            3          27                                                    6            4          42                                                    7            5          50                                                    8            6          63                                                    ______________________________________                                    

The data of Table II show a strong correlation between coating thicknessand uvescent emission level.

EXAMPLE 3

This example describes preparing a solventless epoxysiloxane releasecoating composition containing a chemically bound uvaphore; coating andcuring the release composition on a substrate to yield release liners ofvaried coating weight; and analyzing the release liners on afluorescence spectrophotometer to show the correlation between coatingweight and uvescent emission level.

Into a 12-liter 3-necked round-bottom flask equipped with mechanicalstirrer, pressure equalizing addition funnel, static nitrogenatmosphere, and thermometer was added 5,400 g of a trimethylchain-stopped siloxane fluid composed of 83 mole% dimethylsiloxane unitsand 16 mole% methylhydrogensiloxane units having a viscosity of 200 cps,and 4 liters toluene (see U.S. Pat. No. 4,313,988 for preparation of SiHprepolymers). A solution consisting of 1250 g allylglycidylether, 800 mltoluene, and 1.13 g of a solution composed of 10 wt % chloroplatinicacid and 90 wt % isopropanol was stirred at room temperature for 16.h.before charging to the pressure equalizing addition funnel. The flaskwas heated to 75° C. and maintained at this temperature as the catalyzedallylglycidylether solution was added dropwise over a period of 7 h.Heating was continued for 48 h. before a second solution composed of 120g allylglycidylether, 100 ml toluene, 60 g 9-allylfluorene and 0.375 gof the chloroplatinic acid/isopropanol solution used previously wascharged to the pressure equalizing addition funnel. This secondsolution, containing allylglycidylether and a reactive uvescer, wasadded dropwise over a period of 2 h. and heating was continued for 16 h.more before the completed reaction was cooled to room temperature. Thereaction solution was devolatilized by passing through a thin filmevaporator heated at 90° C. and at a pressure of 0.5 torr over a periodof 8 h. The resultant polymer having the approximate formula ##STR18##was a solventless epoxysiloxane release polymer containing achemically-bound uvaphore, and having a viscosity of 475 cps and anepoxy equivalent weight of 612 g.

An actinic-radiation-activated catalyst was prepared by dissolving 1part of triphenylsulfonium hexafluoroantimonate in a mixture of 25 partsof methylene chloride and 10 parts of ethanol and adding 1 part of fumedsilica (Cab-O-Sil M5™). The mixture was stirred for 15 minutes, filteredto remove solvent and was then air-dried overnight at 25° C. Afterdrying, the silica-supported catalyst was powdered by means of a mortarand pestle and 4 g of this powdered catalyst and 96 g of epoxysiloxanepolymer were mixed together for 10 min. to obtain a solventless UVradiation curing epoxysiloxane release coating composition containing achemically bound uvaphore.

The silicone coating composition was then applied to90-micrometers-thick (3.5 mil) TiO₂ -filled polypropylene film using theequipment and technique described in EXAMPLE 1. The transfer and back-uprolls turned at 30.4 m/min. (100 ft/min.) and the surface speed of thegravure roll was varied from 1.5-4.6 iii/min. (5-15 ft/min.) to provide5 samples of different coating weight. The 5 samples were then passedthrough a UV processing apparatus (consisting of four 30.5 cm (12 inch)medium-pressure mercury lamps, each emitting 120 watts/centimeter) at aspeed of 30.5 m/min to provide samples of cured epoxysiloxane releaseliners. The resultant coating weights were measured using a fluorescentchemical analyzer as in EXAMPLE 1 and the average of 10 measurementsfrom each sample showed average coating weights of the 5 samples to be0.37 g/m², 0.33 g/m², 0.31 g/m², 0.24 g/m²,and 0.10 g/m², respectively.The 5 samples of release liners were then analyzed on a fluorescencespectrophotometer as in EXAMPLE 1 using a λ₁ of 260 nm and a λ₂ of 315nm, except that 8 measurements per sample were taken rather than the 5measurements per sample taken previously. The average fluorescentemission level for each coating weight is recorded in Table III.

                  TABLE III                                                       ______________________________________                                                    Coating     Uvescent                                              Sample      weight (g/m.sup.2)                                                                        emission level                                        ______________________________________                                         9          0.37        85                                                    10          0.33        82                                                    11          0.31        72                                                    12          0.24        49                                                    13          0.10        25                                                    ______________________________________                                    

The data of Table III show excellent correlation between coating weightand uvescent emission level.

EXAMPLE 4

This example describes a solvent based pressure-sensitive acrylicadhesive coating composition containing a soluble, essentiallynon-volatile uvescer; coating and drying the adhesive composition on asubstrate to provide adhesive tapes of varied coating weight; andanalyzing the adhesive tapes on a fluorescence spectrophotometer to showthe correlation between coating weight and uvescent emission level.

To 99.97 9 of a 25% solids 70:30 heptane:isopropanol solution of apressure-sensitive adhesive comprised of 95.5:4.5 isooctylacrylate:acrylic acid copolymer was added 0.03 g 9-allylfluorene. Thissolution was agitated overnight to adequately disperse the uvescer inthe adhesive before coating.

This solution was applied at a variety of coating weights to 51micrometer (2 mil) poly(ethylene terephthalate) film using aconventional knife coating apparatus. Five samples were coated usingorifice settings of 76, 102, 127, 152, and 178 micrometers, respectively(3, 4, 5, 6, and 7 mils, respectively). The coated samples were dried ina forced air oven at 70° C. for 5 minutes to remove solvent and thenanalyzed by gravimetric analysis to obtain coating weights. The coatingweights of the 5 samples were found to be 27.4, 37.3, 43.6, 53.8, and62.4 g/sq.m respectively. These samples were then analyzed on afluorescence spectrophotometer as in EXAMPLE 1 using an excitationwavelength of 253 nm and monitoring uvescent emission at 315 nm. Sixteenmeasurements were taken for each coating and the average uvescentemission level for each coating is reported in Table IV.

                  TABLE IV                                                        ______________________________________                                                    Coating     Uvescent                                              Sample      weight (g/m.sup.2)                                                                        emission level                                        ______________________________________                                        14          27.4        18.6                                                  15          37.3        34                                                    16          43.6        44                                                    17          53.8        75                                                    18          62.4        84.9                                                  ______________________________________                                    

The data of Table IV show excellent correlation between coating weightand uvescent emission level.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

We claim:
 1. A composite structure comprising a substrate bearing anadherent layer of a cured coating composition comprising a polymerhaving chemically bound thereto an effective amount of at least onependent uvaphore that absorbs radiant energy of wavelength λ₁ and emitsradiant energy of λ₂, λ₁ and λ₂ being wavelengths or ranges ofwavelengths within the ultraviolet portion of the electromagneticspectrum, and the mean of the range of λ₂ is above the mean of the rangeof λ₁ in the electromagnetic spectrum, said uvaphore-bearing polymerhaving a product of molar extinction coefficient and quantum yield (εφ)with a value of at least 1,000, wherein said uvaphore is contained in agroup having the formula ##STR19## wherein R is a group comprising atleast one uvaphore and having a valence "a", the uvaphore being apolycyclic aromatic group and having two to four aromatic rings of whichat least two are joined by a single bond or by fusion, the polycyclicaromatic compound absorbing radiant energy of wavelengths between 240and 400 nm, emitting radiant energy below about 430 nm, no more than 30%of the emitted energy being above 400 nm, and having an (εφ) product ofat least 1000,R² is an alkylene or alkenylene group having 1 to 18carbon atoms; Y is a carbon-to-carbon single bond or a divalentconnecting group selected from the group consisting of a carbonyloxygroup, ##STR20## a urethane group, ##STR21## a 3-oxy-2-hydroxypropoxygroup, --OCH₂ CH(OH)CH₂ O--; and a silylethyl group; a is an integerhaving a value one; and b is one.
 2. The composite structure accordingto claim 1 wherein said coating composition has been cured by at leastone of heat, actinic radiation, and electron-beam radiation.
 3. Thecomposite structure according to claim 1 wherein the coating compositionis selected from the group consisting of protective coatings, adhesivecoatings, priming coatings, low adhesion backsize coatings,radiation-sensitive imageable coatings, and release coatings.
 4. Thecomposite structure according to claim 3 wherein said composition is arelease layer.
 5. The composite structure according to claim 1 whereinsaid uvaphore-bearing polymer is the reaction product of a) acondensation or addition polymer having a reactive group with b) auvaphore coupled to a reactive group complementary to the reactive grouppresent in the polymer.
 6. The composite structure according to claim 1wherein said product of molar extinction coefficient and quantum yield(εφ) has a value in the range of 3,000 to 39,800.
 7. The compositestructure according to claim 1 wherein said product of molar extinctioncoefficient and quantum yield (εφ) has a value of at least 3,500.
 8. Thecomposite structure according to claim 1 wherein said product of molarextinction coefficient and quantum yield (εφ) has a value of at least4,400.
 9. The composite structure according to claim 1 wherein saidproduct of molar extinction coefficient and quantum yield (εφ) has avalue of at least 10,000.
 10. The composite structure according to claim1 wherein said substrate luminesces.
 11. The composite structureaccording to claim 1 wherein said uvaphore-bearing polymer is apolyvinylcarbamate, a polyacrylate, a perfluoropolyether, a polyether, apolyester, or a polysiloxane.
 12. The composite structure according toclaim 1 wherein said uvaphore-bearing polymer has a formula selectedfrom the group consisting of ##STR22## wherein j, k and m are integersthe sum of which is 10 to 10,000, k being from 0.01 to 10% of the sum ofj, k and m, m being from zero to 99.5% of the sum of j, k and m, and nbeing an integer from 5 to 10,000, and p and q are integers, the ratioof p/q being 0.2/1 to and the number average molecular weight of the pand q containing polymers being 500 to 20,000.
 13. The compositestructure according to claim 1 wherein said uvaphore-bearing polymer hasa formula selected from the group consisting of ##STR23## wherein R⁶ isindependently selected from the group consisting of one or more of loweralkyl groups (C₁ to C₄) or phenyl groups, and c, d, and e are integers,the sum of which is 10 to 20,000, d is 0.01% to 10% of the sum, and e is5% to 95% of the sum, and p and q are integers, the ratio of p/q being0.2/1 to 5/1 and the number average molecular weights of the polymerscontaining p and q units being 500 to 20,000.